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9-1 Samples and Surveys
Course 3
Warm UpWarm Up
Problem of the DayProblem of the Day
Lesson PresentationLesson Presentation
Warm UpEvaluate.
1. t + 15 for t = –5
2. n + (–13) for n = 7
Solve for x.
3. = –21
4. 7x = –98
10
–6
x = 63
Course 3
9-1 Samples and Surveys
x = –14
x–3
Problem of the Day
Mr. Gray’s 29 students will be sitting in the gym to watch a play. There are two rows of five chairs, three rows of four chairs, and four rows of two chairs. Is there enough room for all the students to sit?yes
Course 3
9-1 Samples and Surveys
Learn to identify sampling methods and to recognize biased samples.
Course 3
9-1 Samples and Surveys
Vocabularypopulationsamplerandom samplesystematic samplestratified sampleconvenience samplevoluntary-response samplebiased sample
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Course 3
9-1 Samples and Surveys
Course 3
9-1 Samples and Surveys
A fitness magazine printed a readers’ survey. Statements 1, 2, and 3 are interpretations. Which do you think the magazine would use?
1. The average American exercises 3 time a week.
2. The average reader of this magazine exercises 3 time a week.
3. The average reader who responded to the survey exercises 3 time a week.
Course 3
9-1 Samples and Surveys
A fitness magazine printed a readers’ survey. Statements 1, 2, and 3 are interpretations. Which do you think the magazine would use?
The population is the entire group being studied. The sample is the part of the population being surveyed.
To get accurate information, it is important to use a good sampling method. In a random sample, each member of the population has an equal chance of being selected. A random sample is best, but other methods can be used.
Course 3
9-1 Samples and Surveys
Sampling Method
How Members are Chosen
Random By chance
Systematic According to a rule or formula
Stratified At random from randomly chosen subgroups
Convenience Easiest to reach
Voluntary-response
Members choose to be in the sample
Course 3
9-1 Samples and Surveys
Additional Example 1A: Identifying Sampling Methods
Identify the sampling method used.
In a county survey, Democratic Party members whose names begin with the letter D are chosen.
systematic The rule is to survey members whose names begin with D.
Course 3
9-1 Samples and Surveys
A telephone company randomly chooses customers to survey about its service.
random Customers are chosen by chance.
Additional Example 1B: Identifying Sampling Methods
Identify the sampling method used.
Course 3
9-1 Samples and Surveys
A high school randomly chooses three classes from each grade and then draws three random names from each class to poll about lunch menus.
stratified The three classes are the random subgroups. Names are chosen randomly from within the classes.
Additional Example 1C: Identifying Sampling Methods
Identify the sampling method used.
Course 3
9-1 Samples and Surveys
Check It Out: Example 1A
Identify the sampling method used.
In a county survey, families with 3 or more children are chosen.
systematic The rule is to survey families with 3 or more children.
Course 3
9-1 Samples and Surveys
A retail home improvement store randomly selects customers to take a survey about their shopping experience.
random Customers are chosen by chance.
Check It Out: Example 1B
Identify the sampling method used.
Course 3
9-1 Samples and Surveys
At a basketball game 5 sections are chosen at random and 20 people from each section are randomly polled.
stratified The five sections are the random subgroups. 20 people are chosen randomly from within the sections.
Check It Out: Example 1C
Identify the sampling method used.
Course 3
9-1 Samples and Surveys
Sometimes, these sampling methods result in biased samples. A biased sample does not accurately represent the population. The data collected from biased samples is not reliable.
Course 3
9-1 Samples and Surveys
Additional Example 2A: Identifying Biased Samples
Identify the population and the sample. Give a reason why the sample could be biased.
A record store manager asks customers who make a purchase how many hours of music they listen to each day.
Record store customers.
Customers who make a purchase.
Customers who make a purchase might be more interested in music than others in the store.
Population Sample Possible Bias
Course 3
9-1 Samples and Surveys
Additional Example 2B: Identifying Biased Samples
An eighth-grade student council member polls classmates about a new school mascot.
Identify the population and the sample. Give a reason why the sample could be biased.
Population Sample Possible Bias
Students in the school
ClassmatesShe polls more eighth-graders than students in other grades.
Course 3
9-1 Samples and Surveys
Additional Example 2C: Identifying Biased Samples
A radio DJ asks listeners for feedback about the type of music played on a radio show.
Identify the population and the sample. Give a reason why the sample could be biased.
Population Sample Possible Bias
People who listen to the radio show
People who hear the question and who call in
The radio only receives feedback from people who listen to that station, and therefore who already enjoy the type of music played on the station.
Course 3
9-1 Samples and Surveys
Check It Out: Example 2A
The first 5 people leaving a movie theater at a sneak preview were asked how they liked the movie.
People that went to the movie
The first five people that left
People that really enjoy a movie are less likely to be one of the first ones to leave.
Population Sample Possible Bias
Identify the population and the sample. Give a reason why the sample could be biased.
Course 3
9-1 Samples and Surveys
Eighth-grade students with a 3.0 GPA or higher were polled to determine how long students study each day.
Eighth grade students
Students with 3.0 or higher GPA
Students with lower grades are less likely to study as long.
Check It Out: Example 2B
Identify the population and the sample. Give a reason why the sample could be biased.
Population Sample Possible Bias
Course 3
9-1 Samples and Surveys
People attending a baseball game were asked if they support the construction of a new stadium in the city.
City residents
People attending a game
People that attend a baseball game are more likely to support the construction of a new stadium.
Check It Out: Example 2C
Identify the population and the sample. Give a reason why the sample could be biased.
Population Sample Possible Bias
Lesson Quiz: Part I
Identify the population and sample. Give areason why the sample could be biased.
1. A high school principal asks the first three people who leave the school play whether they liked it.
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Course 3
9-1 Samples and Surveys
Population Sample Possible Bias
People who attended the play
The first 3 people leaving
People that enjoy a play may not leave as early as someone who didn’t.
Lesson Quiz: Part II
Identify the sampling method used.
2. At a baseball game, 10 sections are chosen at random and 10 random people from each section are polled.
3. A telemarketer calls the people that have a last name beginning with H.
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Course 3
9-1 Samples and Surveys
systematic
stratified
